well. i tried that 2 days back on my friends laptop with Vista on it .Ubuntu installed and worked fine but Vista loader was gone . When i updated grub , Vista entry came there but to no avail. I started recovery tools ! Its very messy to dual boot Vista with ubuntu. You must have a bootable Vista Dvd so that you may apply following fix to recover the bootloader : -
Load up the Windows Vista disc in your drive and press any key to boot from the disc.Choose the language, time etc and click Next. Now click on Repair Your Computer.Choose the operating system to repair and click Next. When the System Recovery Options dialog comes up, choose the Command Prompt.
Now type "bootrec.exe" and press Enter.
After that just type in the following :
"bootrec.exe /fixmbr"
"bootrec.exe /fixboot"
"bootrec.exe /rebuildbcd"
& restart your computer .